1. Field of the Invention
The invention relates to an agitator mill.
2. Background Art
U.S. Pat. No. 4,496,106 discloses an agitator mill that comprises an auxiliary-grinding-body return line discharging from the grinding receptacle upstream of an auxiliary-grinding-body separator device and opening into the grinding chamber at the other end of the grinding receptacle. Directly before this junction, a grinding-stock supply line opens into the auxiliary-grinding-body return line. As a result of the centrifugal effect produced by the agitator unit, the auxiliary grinding bodies and grinding stock not sufficiently milled the to be catapulted off through the auxiliary-grinding-body outlet and returned through the grinding-body return line. By the auxiliary-grinding-body return line opening into the grinding-stock supply line, a suction is to be generated, still supporting the centrifugal effect. Further, excellent preliminary mixing of the grinding stock and the auxiliary grinding bodies is to result in the grinding-stock supply line. Experience has shown that any reliable circulation of the auxiliary grinding bodies cannot be ensured by this design of the known agitator mill. The auxiliary grinding bodies get stuck in the auxiliary-grinding-body return line, where they stay. Although, owing to their basic concept, agitator mills of this type have considerable advantages where a high throughput of grinding stock is required that is marked by a considerable transport of auxiliary grinding bodies in the grinding chamber to the separator device, this type of agitator mills has not been successful in practice, because the circulation of the auxiliary grinding bodies does not work satisfactorily.
An agitator mill is known from U.S. Pat. No. 5,062,577, which has a cylindrical grinding chamber with a likewise cylindrical internal stator. A cup-shaped rotor penetrates the annular space between the wall and the internal stator; the rotor defines an annular outer grinding chamber and an annular inner grinding chamber, which are interconnected by a deflection chamber in the vicinity of the free end of the rotor. Overflow channels are provided in the vicinity of the bottom of the rotor. This is also the portion to which a grinding stock inlet portion is assigned. Further, the portion of these overflow channels is followed, in the direction of flow, by an auxiliary-grinding-body retaining device. Grinding stock is supplied through the grinding-stock inlet portion, flowing together with the auxiliary grinding bodies through the outer grinding chamber, the deflection chamber and the inner grinding chamber, while being milled and dispersed through the rotation of the rotor in cooperation with the auxiliary grinding bodies. Before reaching the auxiliary-grinding-body retaining device, the auxiliary grinding bodies are catapulted off via the overflow channels back into the grinding-stock inlet portion. The grinding stock is discharged via the retaining device. As a result of this embodiment, a grinding-stock fineness is achieved that is extraordinarily uniform, the retaining device simultaneously being largely free from wear, which helps preclude any breakdown.
An agitator mill is known from EP 0 146 852 B1, comprising a grinding receptacle with a cylindrical inner wall and a cylindrical agitator unit, an annular cylindrical grinding chamber being formed between the agitator unit and the inner wall of the grinding receptacle. At its free end, the agitator unit has a cavity, into which projects a separator device. In this area, the agitator unit is provided with recesses all around the separator device, the recesses allowing the auxiliary grinding bodies, which reach the cavity from the front of the free end of the shaft, to be discharged radially into the adjacent grinding chamber. There is the risk of auxiliary grinding bodies compacting in the vicinity of the free shaft end, i.e. around the cavity.
An agitator mill with a vertical agitator unit is known from S.U. patent 737 004. The grinding stock is supplied in the vicinity of the bottom of the grinding receptacle and is discharged under the lid of the grinding receptacle through a filter cylinder. The agitator shaft is hollow and open towards its free end adjacent to the bottom. Several openings are provided along the height of the agitator shaft. This embodiment helps ensure that auxiliary grinding bodies depositing on the bottom move upward through the agitator shaft and are catapulted off into the grinding chamber in a manner distributed along the height of the grinding chamber.